docs: def add_initial(initial_input):
      """
      Constructs a stateful object for handling vensim's 'Initial' functionality
  
      Parameters
      ----------
      initial_input: basestring
          The expression which will be evaluated, and the first value of which returned
  
      Returns
      -------
      reference: basestring
          reference to the Initial object `__call__` method,
          which will return the first calculated value of `initial_input`
  
      new_structure: list
          list of element construction dictionaries for the builder to assemble
  
      """
      stateful = {
          'py_name': utils.make_python_identifier('_initial_%s' % initial_input)[0],
          'real_name': 'Smooth of %s' % initial_input,
          'doc': 'Returns the value taken on during the initialization phase',
          'py_expr': 'functions.Initial(lambda: %s)' % (
              initial_input),
          'unit': 'None',
          'lims': 'None',
          'eqn': 'None',
          'subs': '',
          'kind': 'stateful',
          'arguments': ''
      }
  
      return "%s()" % stateful['py_name'], [stateful]